JP2020512178A - Preparation of filtration membrane - Google Patents

Abstract

A method for preparing a filtration membrane. The method comprises providing a copolymer solution by dissolving a statistical copolymer in a mixture of a co-solvent and a first organic solvent, coating the copolymer solution on a porous support layer to form a polymer layer on the support layer. Forming a thin film composite membrane by coagulating the polymer layer on the support layer, and immersing the thin film composite membrane in a water bath to obtain a filtration membrane. Also disclosed are filtration membranes prepared by the method, as well as processes for filtering liquids using the filtration membranes thus prepared.

Description

  Filtration membranes are of great interest due to their wide application in purification and separation in the food, dairy, beverage and pharmaceutical industries.

  Membranes with high flux (ie, high permeability) and high selectivity are desirable for energy efficient membrane separations. Existing methods for improving membrane flux include grafting and blending. Do these methods require very long manufacturing or post-treatment steps, resulting in a loss of selectivity, or provide only certain membrane types (eg, porous ultrafiltration and microfiltration membranes)? , And thus their use is limited in making filtration membranes with dense selective layers.

  There is a need for new methods of preparing highly permeable and highly selective filtration membranes.

  Disclosed herein is a method of preparing a filtration membrane to meet this need.

  The method comprises the steps of: (i) providing a copolymer solution by dissolving the statistical copolymer in a mixture of a co-solvent and a first organic solvent; (ii) pouring the copolymer solution A high quality support layer to form a polymer layer on the support layer; (iii) solidifying the polymer layer on the support layer to form a thin film composite membrane; and (iv) forming the thin film composite membrane. Soaking in a water bath to obtain a filtration membrane.

  The copolymer solution can be 1-99 w / v% (eg, 1-50 w / v%, and 3-30 w / v%) statistical copolymer, 1-99 v / v% (eg, 1-80 v / v%, and 5). ˜49 v / v%) and a first organic solvent at 1-99 v / v% (eg 20-99 v / v%, and 51-95 v / v%).

  The statistical copolymer comprises zwitterionic repeating units and hydrophobic repeating units, wherein the zwitterionic repeating units make up 15-75 wt% (eg, 20-70 wt%, and 30-50 wt%) of the statistical copolymer. , The hydrophobic repeating unit constitutes 25 to 85% by mass (eg, 30 to 80% by mass, and 50 to 70% by mass) of the statistical copolymer, and the hydrophobic repeating unit has a temperature of 0 ° C. or higher (eg, room temperature or higher). Homopolymers having a glass transition temperature can be formed.

  The cosolvent may be an ionic liquid, a surfactant molecule, or a second organic solvent. Importantly, the cosolvent is miscible with both water and the first organic solvent.

  Examples of first organic solvents include, but are not limited to, trifluoroethanol, dimethylsulfoxide, formamide, dimethylformamide, hexafluoroisopropanol, N-methyl-2-pyrrolidone, pyridine, dioxane, toluene, chloroform, benzene. , Carbon tetrachloride, chlorobenzene, 1,1,2-trichloroethane, dichloromethane, dichloroethane, xylene, tetrahydrofuran, methanol, and ethanol. Examples of second organic solvents include, but are not limited to, trifluoroethanol, hexafluoroisopropanol, dioxane, chloroform, dichloromethane, methylene chloride, dichloroethane, tetrahydrofuran, acetonitrile, 2-butanol, 2-butanone, methanol, And ethanol.

  The coagulation step, step (iii), typically involves a polymer layer (formed after coating the copolymer solution onto the porous support layer) for 60 minutes or less (eg, 10 minutes, and 20 minutes). Sec) air-dried. It involves a coating step, ie, immersing the polymer selective layer together with the porous support layer formed in step (ii) in a non-solvent bath for 60 minutes or less (eg, 20 minutes and 10 minutes). It can also be done by doing. Typically the non-solvent is methanol, ethanol, isopropanol, butanol, acetone, water, or a combination thereof.

  The method may further comprise an annealing step after the dipping step, ie step (iv), wherein the filtration membrane so obtained is subjected to a temperature of 50 ° C. or higher (eg 70 ° C.). , And 90 ° C.) in a water bath.

The filtration membrane prepared by the above method is also within the scope of the present invention. The membrane has an effective pore size of 0.5-5 nm (eg, 0.6-3 nm, and 0.8-2 nm), 10 Lm ⁻² h ⁻¹ bar ⁻¹ or higher (eg, 20 Lm ⁻² h ^−). Water permeability coefficient of ¹ bar ⁻¹ or higher and 30 Lm ⁻² h ⁻¹ bar ⁻¹ or higher).

  The present invention further includes a process of filtering a liquid using the filtration membrane thus prepared.

  The process comprises the following steps: providing a filtration membrane prepared by the above method having a support layer and a polymer selective layer; a liquid is passed first through the polymer selective layer and then through the support layer and through the filtration membrane. And, finally, collecting the liquid that permeates the filtration membrane.

  The details of the invention are set forth in the description below. Other features, objects, and advantages of the invention will be apparent from the following drawings and detailed description of some embodiments, and the appended claims.

It is the schematic of the cross-sectional SEM image of a film. From left to right: uncoated PVDF 400R substrate membrane (Samples 2-5), as well as three modified P40 membranes prepared with different amounts of ionic liquid cosolvent: IL2 (Sample 2-1), IL5. (Sample 2-2) and IL20 (Sample 2-3): cross-sectional SEM images. All samples show a dense coating. Sample 2-1 with the 2% ionic liquid cosolvent shows a dense coating of about 1 μm. Sample 2-2 with the 5% ionic liquid co-solvent shows a dense coating of about 0.7 μm. Sample 2-3 with 20% ionic liquid cosolvent shows a dense coating of about 2.5 μm. Schematic of cross-sectional FESEM image of IL20 film (Sample 2-3) showing the dense copolymer coating. Schematic of the inhibition of charged and neutral molecules of different calculated molecular diameters by neat P40 membrane and modified P40 membrane IL20. Both membranes showed selectivity with a size cutoff of about 0.8-1 nm. Schematic of SEM images of IL20 membranes prepared with different solvent evaporation times during membrane formation. From left to right: IL20_b, 20 seconds dried membrane (Sample 3-1); IL20_c, 2 minutes dried membrane (Sample 3-2); IL20_d, 10 minutes dried membrane (Sample 3-3); and IL20_e, Membrane dried for 20 minutes (Sample 3-4). All samples show a dense coating with a thickness of 1-6 μm. Schematic of FTIR spectra of neat P40 (Sample 2-4, top) and IL20 membrane (Sample 2-3, bottom) air-dried samples. No significant changes in membrane structure or morphology are seen. The spectrum shows that the copolymer layer of the IL20 film is intact.

  First, a method for preparing a filtration membrane with high flux and selectivity is disclosed in detail here.

  Studies with block copolymers (BCP) have included varying copolymer composition (eg, monomer structure and monomer ratios), using additives (eg, homopolymers and metal salts), and mixing solvents (eg, methanol and isopropanol). It is shown that the behavior of the copolymer can be changed and the membrane performance can be improved by adjusting the copolymer casting solution by a certain method, including:

  BCP self-assembly is typically limited to domain sizes of 10-100 nm. See Park et al., Polymer, 2003, 44, 6725-6760. The smallest domain size reported to date is about 3 nm, which is still much larger than that required for membranes with a molecular weight cutoff (MWCO) of less than 5000 g / mol. See Park et al., Science, 2009, 323, 1030-1033.

  Random or statistical copolymers have been reported to function as selective layers for membranes with pore sizes of about 1 nm. See Bengani et al., Journal of Membrane Science, 2015, 493, 755-765. Membranes with a pore size of about 1 nm are very useful for the separation and purification of small molecules in biotechnology, biochemistry, food, beverage and water treatment industries.

  No studies have been reported on the use of co-solvents such as ionic liquids in cast solutions during film formation of random copolymers and how they affect the membrane performance.

  As mentioned above, the method of preparing a filtration membrane encompassed by the present invention provides a copolymer solution by dissolving the statistical copolymer in a mixture of the following steps: (i) a co-solvent and a first organic solvent. (Ii) coating the copolymer solution on a porous support layer to form a polymer layer on the support layer; (iii) solidifying the polymer layer on the support layer to form a thin film composite membrane. And (iv) immersing the thin film composite membrane in a water bath to obtain a filtration membrane.

  The cosolvent used to prepare the copolymer solution is miscible with (miscible with) both water and the first organic solvent. Typically, cosolvents are liquid at temperatures of 100 ° C or lower (eg, 50 ° C or lower, and room temperature or lower). The cosolvent can modify the self-assembly of statistical copolymers in the copolymer solution.

In one embodiment of the method, the cosolvent is an ionic liquid. Ionic liquids are typically ammonium, imidazolium, piperidinium, pyridinium, pyrrolidinium, phosphonium, sulfonium, guanidinium, diethanolammonium, alkylammonium, alkylimidazolium, alkylpiperidinium, alkylpyridinium, alkylpyrrolidinium, alkyl. One or more cations of phosphonium, alkylsulfonium, alkylguanidinium, and alkyldiethanolammonium; and nitrates, sulfonates, methanesulfonates, alkylsulfonates, fluoroalkylsulfonates, sulfates, methylsulfates, alkylsulfates, Fluoroalkyl sulfate, phosphate, methyl phosphate, alkyl phosphate, full Roalkyl phosphate, phosphinate, methyl phosphinate, alkyl phosphinate, fluoroalkyl phosphinate, halogen, trifluoromethanesulfonate, dihydrogen phosphate, bis (trifluoromethylsulfonyl) imide, alkylimide, alkylamide, Includes one or more anions of tetrafluoroborate, hexafluorophosphate, formate, acetate, trifluoroacetate, dicyanamide, decanoate, alkylmethide, and alkylborate. Examples of ionic liquids include, but are not limited to, ethylammonium nitrate (or ethylammonium nitrate), 1-ethyl-3-methylimidazolium ethylsulfate, 1-ethyl-3-methylimidazolium tetrafluoroborate. , 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, 1-butylpyridinium bromide, and 2-hydroxyethyl-dimethylammonium trifluoromethanesulfonate. .

  In another embodiment of the method, the cosolvent is a surfactant molecule. Surfactant molecules are generally sulfate, sulfonate, phosphate, carboxylate, nitrate, or sulfosuccinate anionic groups; and primary amines, secondary amines, tertiary amines, quaternary ammoniums. , Imidazolium, piperidinium, pyridinium, pyrrolidinium, or phosphonium. Examples of surfactant molecules include, but are not limited to, linear alkylbenzene sulfonates, lignin sulfonates, fatty alcohol ethoxylates, alkylphenyl ethoxylates, phospholipids, phosphatidyl serines, phosphatidyl ethanolamines, phosphatidyl cholines, and sphingos. Examples include myelin.

  The copolymer solution is formed from a statistical copolymer containing zwitterionic repeating units and hydrophobic repeating units.

  Each zwitterionic repeat unit may independently include sulfobetaine, carboxybetaine phosphorylcholine, or pyridinium alkyl sulfonate; each hydrophobic repeat unit is independently styrene, fluorinated styrene, methyl methacrylate. , Acrylonitrile, or trifluoroethyl methacrylate. In one embodiment, each zwitterionic repeat unit is independently sulfobetaine acrylate, sulfobetaine acrylamide, phosphoryl choline acrylate, phosphoryl choline acrylamide, phosphoryl choline methacrylate, carboxybetaine acrylate, carboxybetaine methacrylate, carboxybetaine acrylamide. , 3- (2-vinylpyridinium-1-yl) propane-1-sulfonate, 3- (2-vinylpyridinium-1-yl) butane-1-sulfonate, 3- (4-vinylpyridinium-1-yl) propane Formed from -1-sulfonate, or sulfobetaine methacrylate; each hydrophobic repeating unit is independently methyl methacrylate, acrylonitrile, or trifluoroethyl methacrylate It is formed from

  Examples of statistical copolymers formed from the zwitterionic repeating units and the hydrophobic repeating units described above include, but are not limited to, poly ((trifluoroethylmethacrylate) -r- (sulfobetainemethacrylate)), poly ( ((Methylmethacrylate) -r- (sulfobetainemethacrylate)), poly ((trifluoroethylmethacrylate) -r- (3- (2-vinylpyridinium-1-yl) propane-1-sulfonate)), Poly ((trifluoroethylmethacrylate) -r- (phosphorylcholine methacrylate), and poly ((trifluoroethylmethacrylate) -r- (3- (2-vinylpyridinium-1-yl) butane-1-sulfonate) ) Is mentioned.

  In one embodiment of the method, the zwitterionic repeat units make up 30-50% by weight of the statistical copolymer, the hydrophobic repeat units make up 50-70% by weight of the statistical copolymer, and the statistical copolymer is poly ((tri Fluoroethyl methacrylate) -r- (sulfobetaine methacrylate)), the co-solvent is ethyl ammonium nitrate, and the first organic solvent is trifluoroethanol.

  The copolymer solution thus formed can be coated on the porous support layer using any of the methods known in the art (eg, doctor blade coating, spray coating, and dip coating).

  Typically, the solidification step is performed by air-drying the polymer layer for 60 minutes or less (eg, 20 minutes, 10 minutes, 2 minutes, and 20 seconds). It can also be done by soaking the polymer layer in a non-solvent bath for 60 minutes or less (eg 40 minutes, 30 minutes, 20 minutes, and 10 minutes).

  The above method effectively improves membrane flux and permeability by modifying the membrane manufacturing process using the same polymeric material, without sacrificing selectivity and without adding any new steps. To do.

  The filtration membrane prepared by the above method is also disclosed herein in detail.

Membranes prepared by the above method unexpectedly show a permeability coefficient of 30 Lm ⁻² h ⁻¹ bar ⁻¹ or higher, which is greater than that of membranes prepared without cosolvents. It is an order of magnitude higher. Furthermore, the membranes thus prepared maintain selectivity with an effective pore size of 1-2 nm or a MWCO of 1000-5000 Da, as demonstrated by filtering negatively charged dyes and neutral dyes. However, it also shows a narrow pore size distribution. Furthermore, these membranes exhibit low salt retention, for example retention of magnesium sulfate (MgSO ₄ ), in the range of 0-20%. The performance of these membranes depends on the copolymer composition, the type and amount of cosolvent (eg ionic liquid), and the membrane preparation conditions (eg non-solvent and drying time).

  A process for filtering a liquid using the thus-prepared filtration membrane is also within the scope of the present invention.

  As described above, the process comprises three steps: (i) providing a filtration membrane prepared by the above method having a support layer and a polymer selective layer; (ii) passing the liquid through the polymer selective layer first. And (iii) collecting the liquid that permeates the filtration membrane, and then passing the filtration membrane through the support layer.

  Examples of applications of the process of the invention include, but are not limited to, separation of a mixture of two dyes or solutes having similar charges but different sizes, separation of two water-soluble organic molecules having different sizes. , Separation of mixtures of monomers and oligomers dissolved in water, separation of mixtures of peptides, dietary supplements, antioxidants and other small molecules dissolved in water, wastewater treatment, treatment of natural water sources (eg surface and ground water) ), As well as the removal of ions from water.

  Without further elaboration, those skilled in the art will be able to make the best use of the present invention based on the above description. Therefore, the following specific examples should be construed as merely illustrative and not in any way limiting of the rest of this disclosure. The publications mentioned herein are incorporated by reference in their entirety.

Example 1 : Preparation of statistical copolymer poly (trifluoroethyl methacrylate-random-sulfobetaine methacrylate) (PTFEMA-r-SBMA or P40) In this example, Bengani et al., Journal of Membrane Science, 2015, 493. Statistical copolymers were synthesized according to the protocol reported in 755-765.

More specifically, 2,2,2-trifluoroethyl methacrylate (TFEMA, Sigma Aldrich) was passed through a column of basic activated alumina (VWR) to remove the inhibitor. Sulfobetaine methacrylate (SBMA; 5 g, 17.9 mmol) was dissolved in dimethyl sulfoxide (DMSO, 100 ml) in a round bottom flask with stirring at 350 rpm. TFEMA (5 g, 29.7 mmol) and the thermal initiator azobisisobutyronitrile (AIBN, 0.01 g, Sigma Aldrich) were added to the flask. The flask was sealed with a rubber septum and nitrogen was bubbled through the contents of the flask for 20 minutes to purge dissolved oxygen. The flask was then placed in a 70 ° C. oil bath with stirring at 350 rpm. After at least 16 hours, 0.5 g of 4-methoxyphenol (MEHQ) was added to terminate the reaction. The reaction mixture was precipitated in a 50:50 mixture of ethanol and hexane. The product is vacuum filtered, residual solvent and monomers are extracted by stirring the polymer in two fresh methanol for several hours, then dried in a vacuum oven at 50 ° C. overnight to give the copolymer PTFEMA-r-SBMA. It was The composition of this white copolymer was calculated from the ¹ H-NMR spectrum using the ratio of total backbone protons (0.5-2 ppm) to SBMA protons (2-3.5 ppm). The copolymer thus obtained was identified to contain 36% by weight of SBMA.

Example 2 : Preparation of modified P40 copolymer membranes prepared with different amounts of ionic liquid In this example, how many of the copolymers described in Example 1 were used in the presence or absence of ionic liquid as follows: The membrane was prepared.

  More specifically, an ionic liquid, ethylammonium nitrate (EAN, Iolitec) was dissolved in trifluoroethanol. The copolymer (1 g) was dissolved in 9 mL total solvent content (ionic liquid and trifluoroethanol), thus keeping the copolymer concentration constant at 10% (w / v) to form a copolymer solution. Mixing 0 mL, 0.2 mL, 0.5 mL, and 2 mL of the ionic liquid into 9 mL, 8.8 mL, 8.5 mL, and 7 mL of trifluoroethanol, respectively, and further dissolving 1 g of the copolymer in each. To prepare P40, IL2, IL5 and IL20 solutions. The copolymer solution was stirred at approximately 50 ° C. for at least 2 hours to prepare a 10% (w / v) copolymer cast solution. Each copolymer casting solution was passed through a 0.45 μm syringe filter (Whatman) and degassed in a vacuum oven for an additional 2 hours. Membranes were prepared by coating a thin layer of copolymer casting solution onto a commercial ultrafiltration (UF) membrane using a 25 μm doctor blade gap. Polyvinylidene fluoride (PVDF) 400R ultrafiltration membrane purchased from Nanostone Water (Eden Prairie, MN) was used as the base membrane. After coating, the membranes were dipped in isopropanol, a polar non-solvent bath for 20 minutes and then in a water bath for at least overnight. Being water-soluble, the ionic liquid was efficiently removed in a water bath and the membrane was transferred to another water bath for storage.

  The thickness and morphology of the coating was determined by inspecting the freeze fractured cross section using a scanning electron microscope (SEM). See FIG.

  This figure shows, from left to right, SEM images of an uncoated PVDF400R substrate membrane and three modified P40 membranes prepared with ionic liquids: IL2, IL5, and IL20: all at the same magnification. is there. Compared to the SEM image of the PVDF400R substrate film, the SEM images of IL2, IL5 and IL20 show a dense coating layer (ie, with a thickness of about 0.5-3 μm formed using a doctor blade gap of 25 μm). No coarse pores or macrovoids). The coating thickness varies between 0.5 and 3 μm for a given doctor blade gap size depending on the amount of ionic liquid in the copolymer casting solution.

  The morphology of the coating of the IL20 membrane (Sample 2-3) was further characterized by examining the freeze-fractured cross section of the membrane using field emission scanning electron microscopy (FESEM). See FIG. FESEM of IL20 shows that a dense coating layer was formed.

Example 3 : Water permeability of modified P40 copolymer membranes prepared with different amounts of ionic liquid In this example, the pure water flux through the membrane described in Example 2 was measured as follows.

This test was performed using an Amicon 8010 stirred total volume filtration cell (Millipore) with a cell volume of 10 mL and an effective membrane filtration area of 4.1 cm ² . The cell was continuously agitated and tested at 10 psi (0.7 bar). Permeate samples were collected at regular intervals after a stabilization period of at least 1 hour. Permeate mass was measured with a Scout Pro SP401 balance connected to a Dell laptop that automatically measures every 30 seconds using TWedge 2.4 software (TEC-IT, Austria). Flux is calculated by dividing the permeate volume by the filtration area and the experimental time. The pure water permeability coefficient is obtained by normalizing the flux value with pressure (see Table 1 below).

  The permeance and permeability of water for neat P40 membranes and modified P40 copolymer membranes prepared with different amounts of ionic liquid during membrane formation are shown in Table 1 below. Tests were performed on neat P40 membrane (Sample 2-4) and on three modified P40 membranes, both IL2 (Sample 2-1), IL5 (Sample 2-2) and IL20 (Sample 2-3). did.

The permeation coefficient of neat P40 membrane is 6.1 ± 1 L / m ² h. It was found that the modified P40 membrane IL20 had a permeability coefficient of 50 ± ² L / m ² h. It was found to be higher than bar, i.e. an order of magnitude higher than neat P40 membrane. The neat P40 membrane has a permeability of 6.4 ± 1L. μm. / M ² h. The permeability of the IL20 membrane, despite its thicker coating, was found to be 125 ± 5 L. μm. / M ² h. It was found to be higher than bar, i.e. two orders of magnitude higher than neat P40 membrane. The permeability of the IL20 membrane was much higher than the commercial nanofiltration membrane (NF) membrane, despite its thick coating. The IL20 membranes tested had a coating that was always> 2.5 μm thick. In comparison, commercially available NF membranes have selective layers as thin as <0.1 μm. The permeation coefficient of the PVDF 400R base material membrane is 200 + 20 L / m ² h. It is bar.

The permeability coefficients of the IL2 and IL5 membranes are 0.7 ± 0.2 L / m ² h. bar and 1.7 ± 0.7 L / m ² h. bar, ie, the coating thickness is similar or slightly thinner for the IL5 membrane, but slightly lower than the permeability coefficient of neat P40 membranes prepared without any cosolvents. I understood. This indicates that for the particular membrane described in Example 2, too low an ionic liquid content (≦ 5%) did not increase or decrease the water permeability through the copolymer layer at all. The coating prepared with 50% ionic liquid content in the casting solution resulted in poor integrity of the coating in water. This means that for a given copolymer composition (ie, the ratio of zwitterionic and hydrophobic repeat units in the copolymer), the increase in membrane permeability results in a specific range of ionic liquid concentration (ie, ionic liquid in the casting solution). Volume).

Example 4 : Dye Inhibition of P40 Membrane and Modified P40 Copolymer Membrane IL20 In this example, membranes prepared as described in Example 2 were used with negatively charged solutes and neutral solutes (pigments and vitamins). The effective pore size or size cutoff value of

These solutes were used because they are hard and their concentration can be easily and accurately measured by UV-visible spectroscopy. Solute inhibition experiments were performed on an Amicon 8010 stirred total volume filtration cell (Millipore) with a cell volume of 10 mL and an effective membrane filtration area of 4.1 cm ² . In order to explain the difference in the membrane permeability coefficient between the P40 membrane and the modified P40 membrane IL20, 6.1 L. m ^-2 . The test was carried out at a constant initial water flux of hr ⁻¹ (equal to the initial flux of P40 membrane). This pressure was kept constant throughout the experiment even though the membrane flux was reduced when solute was introduced. The cell was continuously stirred to minimize the effect of concentration polarization. After passing pure water through the membrane for at least 1 hour, the cell was emptied and filled with a 100 mg / L aqueous solution of probe solute. After discarding the first 1 ml, the next 1 ml sample was collected for analysis by UV-Vis spectroscopy. The cell was washed several times with deionized water. Prior to exchange with fresh probe solute, deionized water was filtered through the membrane until the permeate was clear. FIG. 3 shows the retention of various negatively charged and neutral solutes by the neat P40 membranes (Samples 2-4) and IL20 membranes (Samples 2-3) described in Examples 2 and 3.

The molecular size and charge of the solutes used to test the effective membrane size cutoff and their inhibition by neat P40 and IL20 membranes are shown in Table 2 below.

  The solute diameters shown in Table 2 above were calculated based on the molecular volume values obtained by Molecular Modeling Pro software by ChemSW, using the calculated molecular volumes and fitting the corresponding volume range to this value. . Based on the filtration of these anionic and neutral solutes, the size cutoff of membranes prepared with ionic liquid cosolvents was found to be between 0.8 nm and 1 nm, as shown in Table 2, The blocking of these solutes was more directly related to the solute's molecular size than its charge.

  Essentially, there was no measurable change in pore size between neat P40 membrane and modified P40 membrane IL20. The IL20 membrane was unexpectedly found to exhibit a narrow pore size distribution, and such a narrow pore size distribution is particularly difficult to achieve with membranes in this pore size range. More importantly, the use of an ionic liquid as a co-catalyst in the copolymer casting solution resulted in an unexpected 10-fold improvement in flux while maintaining its selectivity. This method of membrane production is very beneficial, as few methods are known to improve membrane permeation flux without sacrificing pore size.

  Among the membranes prepared with different amounts of ionic liquid co-solvents, the IL20 membrane has the highest permselectivity, while maintaining its selectivity, it has a permeability coefficient of 10 compared to the neat P40 membrane. It brought a double rise. At this stage of screening, the IL20 membrane was selected as the primary candidate for further testing.

Example 5 : Salt Inhibition by Modified P40 Copolymer Membrane Prepared with Different Amounts of Ionic Liquid Cosolvents In this example, a membrane prepared as described in Example 2 was used in a retention test as follows. To determine their salt retention properties.

Retention tests were carried out on an Amicon 8010 stirred total volume filtration cell (Millipore; filtration device with specific capacity) with a cell volume of 10 mL and an effective membrane filtration area of 4.1 cm ² . Due to the difference in the membrane permeation coefficient of P40 membrane and modified P40 membrane IL20, tests were conducted under constant initial flux conditions. The cell was continuously stirred to minimize the effect of concentration polarization. After passing pure water through the membrane for at least 1 hour, the cell was emptied and filled with 200 mg / L magnesium sulfate (MgSO ₄ , Aldrich) solution. After the first equilibration period, the filtrate was collected for analysis by standard conductivity probe. The cell was washed several times with water and pure water was passed through the membrane before it was replaced with another feed solution.

The retention of the MgSO ₄ salt was 17.4% with the neat P40 membrane and unexpectedly less than 10% with the modified P40 membranes (IL2, IL5, and IL20).

Example 6 : Formation of Modified P40 Copolymer (IL20) Membrane Using Different Solvent Evaporation Times During Membrane Formation In this example, several membranes were prepared with IL20 casting solution as follows.

  An IL20 solution was prepared by mixing 2 ml of the ionic liquid (ethylammonium nitrate) in 7 ml of trifluoroethanol and dissolving 1 g of P40 copolymer therein. The copolymer solution was stirred at approximately 50 ° C. for at least 2 hours to prepare a 10% (w / v) copolymer cast solution. The copolymer casting solution was passed through a 0.45 μm syringe filter (Whatman) and degassed in a vacuum oven for an additional 2 hours. Membranes were prepared by coating a thin layer of copolymer casting solution onto a commercial ultrafiltration (UF) membrane using a 25 μm doctor blade gap. A PVDF400R ultrafiltration membrane purchased from Nanostone Water (Eden Prairie, MN) was used as the substrate membrane. After coating, it was air dried for different times and then soaked in a water bath for at least overnight. The selected drying time ranged from a few seconds to 20 minutes. IL20_b, IL20_c, IL20_d, IL20_e thin film composite membranes were prepared with solvent evaporation times of 20 seconds, 2 minutes, 10 minutes and 20 minutes, respectively. Being water-soluble, the ionic liquid additive was efficiently removed in the water bath and the membrane was transferred to another water bath for storage.

  The thickness and morphology of the coating was determined by inspecting the freeze-fractured section of the film using a scanning electron microscope (SEM). See FIG.

  SEM images were obtained at all the same magnification for four films IL20_b, IL20_c, IL20_d, IL20_e formed from the IL20 copolymer solution using different drying times during film formation. From left to right in FIG. 4, IL20_b, membrane dried for 20 seconds (Sample 3-1); IL20_c, membrane dried for 2 minutes (Sample 3-2); IL20_d, membrane dried for 10 minutes (Sample 3-3); And IL20_e, 20 minutes dried membrane (Sample 3-4). SEM images of all four films show a dense coating layer (ie, no coarse pores or macrovoids). The coating thickness varies between 1 μm and 6 μm for a given doctor blade gap size, depending on the drying time during film formation.

Example 7 : Water Permeability of Modified P40 Copolymer Membrane IL20 Prepared Using Different Solvent Evaporation Times During Membrane Formation In this example, pure water flux through the membranes described in Examples 2 and 6 as follows: Was measured using an Amicon 8010 stirred total volume filtration cell (Millipore) with a cell volume of 10 mL and an effective membrane filtration area of 4.1 cm ² .

  The cell was continuously agitated and tested at 10 psi (0.7 bar). Permeate samples were collected at regular intervals after a stabilization period of at least 1 hour. Permeate mass was measured with a Scout Pro SP401 balance connected to a Dell laptop that automatically measures every 30 seconds using TWedge 2.4 software (TEC-IT, Austria). Flux is calculated by dividing the permeate volume by the filtration area and the experimental time. The pure water permeability coefficient is obtained by normalizing the flux value with pressure (see Table 3 below).

  The water permeability coefficient and permeability of membranes prepared with the IL20 copolymer cast solution by different membrane manufacturing methods are shown in Table 3 below. IL20 membranes (Samples 3-1, 3-2, 3-3 and 3-4) prepared with different drying times during membrane formation, and prepared by direct immersion in a non-solvent bath without drying. The test was performed on an IL20 film (Sample 2-3).

  IL20_c, IL20_d, IL20_e membranes (Samples 3-2, 3-3, and 3-4; Table 3) prepared using various drying times of at least 2 minutes during membrane formation were more than the permeability coefficient of IL20. It turned out to be quite low. The permeability coefficient of IL20_b membranes (Sample 3-1, Table 3) prepared with a short drying time of 20 seconds during membrane formation was unexpectedly an order of magnitude higher than neat P40 membranes and prepared by non-solvent immersion. The permeation coefficient was similar to that of the prepared IL20 membrane (Sample 2-3, Table 3). This indicates that a fast drying time (20 seconds) during membrane formation or isopropanol immersion has a high permeability coefficient, which is unexpectedly much higher than commercial nanofiltration (NF) membranes despite thicker coatings. Shows that it gave a membrane. The IL20 membranes tested always had a coating> 1 μm thick. In comparison, commercially available NF membranes have selective layers as thin as <0.1 μm. In fact, higher flux can be obtained with these membranes by using the coating method described above.

Example 8 : Fourier Transform Infrared Spectroscopy of Neat P40 and Modified P40 Membrane (IL20) In this example, of the copolymer coating on membrane sample 2-3 prepared as described in Example 2 as follows. Presence was analyzed using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy.

  FTIR spectra of air dried samples of neat P40 membrane and modified P40 membrane IL20 were compared. See FIG. The spectrum of the IL20 membrane shows no additional peaks, indicating that the ionic liquid was completely removed when the membrane was immersed in deionized water prior to any membrane testing.

Example 9 : Bubble Point Measurements of Neat P40 and Modified P40 Copolymer Membrane (IL20) In this example, the integrity of the copolymer coating on membrane sample 2-3 prepared as described in Example 2 was as follows. And integrity was analyzed using the bubble point test.

  As an index of the maximum pore size present on the membrane surface, a simple lab-scale bubble point measurement was performed using PVDF400R substrate membrane (Sample 2-5), neat P40 (Sample 2-4), and modified P40 membrane (IL20, sample). 2-3) Performed on the sample. The membrane sample is wetted with water and included in the system and the pressure is slowly increased until the first continuous bubble is observed at the outlet. The minimum pressure required to drive water out of the pores is a measure of the maximum pore size in the membrane. The bubble point of PVDF400R was 6 psi (about 0.41 bar), but the bubble point of neat P40 and modified P40 membrane (IL20) was quite continuous up to at least 60 psi (about 4.1 bar) (ie the upper detection limit of the device). It was observed that there was no indication of bubble formation. This indicates that the copolymer coating is undamaged and lacks the coarse pores or exposed areas of the PVDF400R substrate membrane and does not contribute to the 10-fold higher flux increase seen in the modified P40 membrane (IL20).

Example 10 : Contact Angle of Neat P40 and Modified P40 Copolymer Membrane (IL20) In this example, a goniometer was used to determine the surface properties of Membrane Samples 2-3 prepared as described in Example 2.

  As a measure of the hydrophilicity of the material, the trapped bubble contact angle measurement was performed by completely immersing the sample in neat P40 membrane (Sample 2-4) and three modified P40 membranes IL2 (Sample 2-1) and IL5 (Sample). 2-2) and IL20 (Sample 2-3). The contact angle of neat P40 membrane was observed to be about 29.3 ± 3 °, whereas the contact angles of modified P40 membranes IL2, IL5, and IL20 were unexpectedly 26.7 ± 3 °, 26, respectively. It was found to be 0.3 ± 2 ° and 25.9 ± 4 °. There was no apparent change in the contact angle of the modified P40 samples, including IL20, indicating that the hydrophilicity of the copolymer coating was not significantly affected by the use of ionic liquids during film formation.

Other Embodiments All of the features disclosed in this specification may be combined in any combination. Each feature disclosed in this specification may be replaced by an alternative feature serving the same, equivalent, or similar purpose. Therefore, unless expressly stated otherwise, each feature described is merely an example of a comprehensive set of equivalent or similar features.

  Further, from the above description, those skilled in the art can easily understand the essential features of the present invention, and can make various changes and modifications of the present invention without departing from the spirit and scope of the present invention. It can be adapted to various applications and conditions. Therefore, other embodiments are also within the claims.

Claims (30)

A method for preparing a filtration membrane, comprising:
Providing a copolymer solution by dissolving the statistical copolymer in a mixture of a co-solvent and a first organic solvent,
Coating the copolymer solution onto a porous support layer to form a polymer layer on the support layer,
Solidifying the polymer layer on the support layer to form a thin film composite membrane, and immersing the thin film composite membrane in a water bath to obtain a filtration membrane,
Including,
The copolymer solution comprises 1-99 w / v% cosolvent, and 1-99 v / v% first organic solvent,
The statistical copolymer includes a zwitterionic repeating unit and a hydrophobic repeating unit, the zwitterionic repeating unit constitutes 15 to 75% by weight of the statistical copolymer, and the hydrophobic repeating unit is 25 to 85% by weight of the statistical copolymer. %, And the hydrophobic repeating unit can form a homopolymer having a glass transition temperature of 0 ° C. or higher, and the cosolvent is miscible with both water and the first organic solvent. Method.   The method of claim 1, wherein the cosolvent is an ionic liquid, a surfactant molecule, or a second organic solvent.   The method of claim 2, wherein the cosolvent is liquid at a temperature of 100 ° C. or lower.   4. The method of claim 3, wherein the cosolvent is liquid at room temperature or below.   The method of claim 2, wherein the cosolvent is an ionic liquid.   The ionic liquid is ammonium, imidazolium, piperidinium, pyridinium, pyrrolidinium, phosphonium, sulfonium, guanidinium, diethanolammonium, alkylammonium, alkylimidazolium, alkylpiperidinium, alkylpyridinium, alkylpyrrolidinium, alkylphosphonium, alkylsulfonium. , Alkylguanidinium, and alkyldiethanolammonium; and nitrates, sulfonates, trifluoromethanesulfonates, alkylsulfonates, fluoroalkylsulfonates, sulfates, methylsulfates. , Alkylsulfate, fluoroalkylsulfate, phosphate, methylphosphate , Alkyl phosphate, fluoroalkyl phosphate, phosphinate, methyl phosphinate, alkyl phosphinate, fluoroalkyl phosphinate, halogen, trifluoromethanesulfonate, dihydrogen phosphate, bis (trifluoromethylsulfonyl) imide, Contain one or more anions selected from the group consisting of alkylimides, alkylamides, tetrafluoroborate, hexafluorophosphate, formate, acetate, trifluoroacetate, dicyanamide, decanoate, alkylmethide, and alkylborate. The method according to claim 5.   The ionic liquid is ethyl ammonium nitrate, 1-ethyl-3-methylimidazolium ethylsulfate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 7. The method of claim 6 selected from the group consisting of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, 1-butylpyridinium bromide, and 2-hydroxyethyl-dimethylammonium trifluoromethanesulfonate.   The method of claim 2, wherein the co-solvent modifies the self-assembly of statistical copolymers in the copolymer solution.   The method of claim 2, wherein the cosolvent is a surfactant molecule.   The surfactant molecule is a cationic group formed from a primary amine, a secondary amine, a tertiary amine, a quaternary ammonium, an imidazolium, a piperidinium, a pyridinium, a pyrrolidinium, or a phosphonium; and a sulfate or a sulfonate. 10. The method of claim 9, comprising an anionic group selected from the group consisting of, phosphates, carboxylates, nitrates, and sulfosuccinates.   The surfactant molecule is selected from the group consisting of linear alkylbenzene sulfonates, lignin sulfonates, fatty alcohol ethoxylates, alkylphenyl ethoxylates, phospholipids, phosphatidylserines, phosphatidylethanolamines, phosphatidylcholines, and sphingomyelins. The method according to claim 10.   2. The method of claim 1, wherein the copolymer solution comprises 1-50 w / v% statistical copolymer, 1-80 v / v% cosolvent, and 20-99 v / v% first organic solvent.   13. The method of claim 12, wherein the copolymer solution comprises 3-30 w / v% statistical copolymer, 5-49 v / v% cosolvent, and 51-95 v / v% first organic solvent.   The zwitterionic repeating units make up 20-70% by weight of the statistical copolymer, the hydrophobic repeating units make up 30-80% by weight of the statistical copolymer, and the hydrophobic repeating units have a glass transition temperature above room temperature. The method of claim 1, wherein a homopolymer having can be formed.   15. The method of claim 14, wherein the zwitterionic repeating units make up 30-50% by weight of the statistical copolymer and the hydrophobic repeating units make up 50-70% by weight of the statistical copolymer.   Each said zwitterionic repeating unit independently comprises sulfobetaine, carboxybetaine phosphorylcholine, or pyridinium alkyl sulfonate; and each said hydrophobic repeating unit is independently styrene, fluorinated styrene, methyl methacrylate. 2. The method of claim 1, formed from acrylonitrile, acrylonitrile, or trifluoroethyl methacrylate.   The zwitterionic repeating units are each independently sulfobetaine acrylate, sulfobetaine acrylamide, phosphoryl choline acrylate, phosphoryl choline acrylamide, phosphoryl choline methacrylate, carboxybetaine acrylate, carboxybetaine methacrylate, carboxybetaine acrylamide, 3- ( 2-Vinylpyridinium-1-yl) propane-1-sulfonate, 3- (2-vinylpyridinium-1-yl) butane-1-sulfonate, 3- (4-vinylpyridinium-1-yl) propane-1-sulfonate , Or sulfobetaine methacrylate; and each of the hydrophobic repeat units is independently methylmethacrylate, acrylonitrile, or trifluoroethylmethacrylate. It is formed, the method according to claim 16.   The statistical copolymer is poly ((trifluoroethylmethacrylate) -r- (sulfobetainemethacrylate)), poly ((methylmethacrylate) -r- (sulfobetainemethacrylate)), poly ((trifluoroethylmethacrylate). (Rat) -r- (3- (2-vinylpyridinium-1-yl) propane-1-sulfonate)), poly ((trifluoroethylmethacrylate) -r- (phosphorylcholine methacrylate), or poly ((trifluoro). 18. The method according to claim 17, which is ethylmethacrylate) -r- (3- (2-vinylpyridinium-1-yl) butane-1-sulfonate).   The first organic solvent is trifluoroethanol, dimethyl sulfoxide, formamide, dimethylformamide, hexafluoroisopropanol, N-methyl-2-pyrrolidone, pyridine, dioxane, toluene, chloroform, benzene, carbon tetrachloride, chlorobenzene, 1 The method of claim 1, wherein the method is selected from the group consisting of, 1,2-trichloroethane, dichloromethane, dichloroethane, xylene, tetrahydrofuran, methanol, and ethanol.   The cosolvent is a second selected from the group consisting of trifluoroethanol, hexafluoroisopropanol, dioxane, chloroform, dichloromethane, methylene chloride, dichloroethane, tetrahydrofuran, acetonitrile, 2-butanol, 2-butanone, methanol, and ethanol. The method according to claim 2, which is the organic solvent of.   The zwitterionic repeating units make up 30-50% by weight of the statistical copolymer, the hydrophobic repeating units make up 50-70% by weight of the statistical copolymer, and the statistical copolymer is poly ((trifluoroethylmethacrylate)). -R- (sulfobetaine methacrylate)), said co-solvent is ethyl ammonium nitrate, and said first organic solvent is trifluoroethanol.   The coagulation step is performed by air-drying the polymer layer for 60 minutes or less, or by soaking the polymer layer in a non-solvent bath with the porous support layer for 60 minutes or less. The method of claim 1, wherein the method is:   23. The method of claim 22, wherein the coagulating step is performed by air drying the polymer layer for 60 minutes or less.   23. The method of claim 22, wherein the coagulating step is performed by soaking the polymer layer with the porous support layer in a non-solvent bath for 60 minutes or less.   25. The method of claim 24, wherein the non-solvent is methanol, ethanol, isopropanol, butanol, acetone, water, or a combination thereof.   The porous support layer has an effective pore size larger than the effective pore size of the polymer layer, and, polyether sulfone, polyphenylene sulfone, polyphenylene sulfide sulfone, polyacrylonitrile, cellulose ester, polyphenylene oxide, polypropylene, polyvinylidene fluoride, The method of claim 1, formed by polyvinyl chloride, polyallyl sulfone, polyphenylene sulfone, polyether ether ketone, polysulfone, polyamide, polyimide, or combinations thereof.   27. The method of claim 26, wherein the porous support layer is a flat sheet membrane or a hollow fiber membrane.   The method according to claim 1, further comprising an annealing step of annealing the obtained filtration membrane in a water bath at a temperature of 50 ° C. or higher after the immersion step. A filtration membrane prepared by the method according to claim 1, having an effective pore size of 0.5 to 5 nm and a water permeability coefficient of 10 Lm ⁻² h ⁻¹ bar ⁻¹ or more. The process of filtering a liquid,
30. Providing a filtration membrane according to claim 29 having a support layer and a polymer selective layer;
Passing a liquid first through the polymer selective layer and then through a support layer through the filtration membrane; and collecting the liquid that permeates the filtration membrane;
Including the process.

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